Abstract: An undercutting knife for a sod cutting machine. The knife has an undercutting blade having a front portion and an upwardly bent rear portion. Connected to the rear portion are two support and guide members, one at each edge of the blade. Each support and guide member extends rearwardly from the blade and has a rear portion projecting laterally of the blade. Mounting arms are connected to the laterally extending portions. The mounting arms, which are connected to mechanism for supporting and reciprocating the knife, are clear of the ground and are spaced laterally of cut sod moving over the knife, so as not to tear the edges of the sod. A guide strip extends rearwardly from the blade between the support and guide members. The support and guide members and the guide strip can be three discrete members or a single integral unit.